This project is a study of the role of sensory inputs in the cerebral control of motor behavior in the primate. It uses the technique of single neuron recording in behaving monkeys to directly compare the activity of neurons in primary motor cortex (MI) during the performance of learned arm movements with the activity of neurons in the parts of the somatic sensory (SI), parietal and frontal cortex which are reciprocally connected with MI. Two questions form the focus of our investigations. First, the possible modulation of peripheral inputs to the sensorimotor cortex during motor activity is being studied by recording SI and MI response to peripheral stimuli delivered during and before active movements, during different levels of steady state motor activity related to differences in the exerted force or length of the contracting muscles and during isometric versus isotonic contractions in which the animal controls either exerted force or arm position. Second, the relation of posterior parietal and frontal cortical areas to visually guided movements is being investigated by determining whether the neuronal activity in these areas reflect information concerning the visual cue to begin movement, as well as limb position or exerted force.